Radio direction finder



March 5, 1940. E. scHuLz 2,192,531,

RADIO DIRECTION FINDER Filed Dec. 12, 193e Enventor Bg l (Ittorneg Patented Mar. 5, 1940 STATESl PATENT OFFCE RADIO DIRECTION FINDER ration of Germany Application December 12, 1938, Serial No. 245,265 In Germany December 11, 1937 3 Claims.

(Cl. Z50-11) (Granted under the provisions of sec. 14, act of March 2, 1927; 357 O. G.

This invention relates to radio direction finders and more particularly to a radio direction nder in which a cathode ray tube is used as the directional indicator.

Radio direction finders employing pairs of directional antennas, separate receivers connected thereto, and a suitably connected cathode ray indicator have been used. In these devices the cathode ray deiiecting electrodes are arranged in space to correspond to the directional antenna patterns so that the cathode ray beam is deflecting along a line determinant of the direction of the incoming signal waves.

There are inherent drawbacks, in the above described prior art direction nders, which have limited the practical use of these devices. For example, the directional indications are accurate only if the gains of the receivers associated with the directional antenna remain absolutely alike. It is difficult to maintain this condition for -any great length of time. Since the cathode ray deiiections are a function of the applied deflecting potentials, it follows that relative variations of gain of the receivers, applyingr the deflecting potentials, will result in variations in deections.

According to the present invention, the diiiculties inherent in the prior art systems are obviated by transposing the receiver connections at a rate preferably above thirty cycles per second. Furthermore, in some uses receivers or amplifiers having dissimilar gains may be employed.

The invention is described by referring to the accompanyingr drawing in which Figure 1 is a schematic circuit diagram of one embodiment of the invention; Figure 2 is an illustration of the cathode ray trace of a prior art directional indicator; and Figure 3 is an illustration of the cathode ray traces obtained by an 4application of the present invention.

Referring to Fig. 1, loop antennas a, b, which are mounted at an angle of 90 with reference to each other, are connected through change-over switches c, d to the inputs of receivers e, f, respectively. 'I'he outputs of the receivers are connected through change-over switches g, h, respectively, to the deiiecting elements lc-7c, m-m of a cathode ray tube n. The change-over switches, c, d and g, h, are interlocked and are connected to any suitable means for operating the switches in synchronism at the predetermined rate.

The operation of the direction iinder is as follows: The potentials established by a signal in the loop a are applied, in the switch position shown, through the receiver e and switch g to the cathode ray deecting electrodes o-lc. At

the same time the potentials established in the loop b are applied through switch d, the receiver f, and switch h to the cathode ray deflecting electrodes mm. When the interlocked changef over switches c, d and y, h are moved to their second position, the potentials from loop a are applied through the second receiver f to the deecting electrodes k-lc; and the potentials from the loop b are applied through the rst receiver e to the deflecting electrodes m-m. Thus, the receivers are interchanged.

The cathode ray traces may be described as follows: In the prior art device, if the two receivers or ampliers apply deflecting potentials not of the same phase, an elliptical trace, such as r of Fig. 2 is obtained. In the present device, the interchange of the receivers by means of the switches c, d, g, h will result in two traces o, q, which will be elliptical as shown in Fig. 3 if the phases of the potential applied at the specied rate to the delecting electrodes are not equal. The ellipses are shifted in opposite directions in comparison with the ellipse r. The line s connecting the intersection of the two ellipses o and q will coincide roughly with the major axis of the ellipse 1'. It should be understood that the line s indicates the direction of the received wave front and hence the direction of the transmitter of the wave. The screen of the cathode ray tube may be suitably calibrated to indicate such direction.

The foregoing arrangement provides a directional indication which is substantially independent of the gain characteristics of the receivers inasmuch as the intersecting line s is substantially independent of the relative positions of the two ellipses o and q. The invention is not restricted to frame or loop aerials and may employ any directional aerial.

I claim:

1. A radio direction nder including pairs of directive antennas arranged so that their directive patterns cross, a pair of radio receivers, switches connected to said antennas and arranged to connect the respective antennas to the inputs of iirst one, then the other of said radio receivers, a cathode ray tube including pairs of deflecting electrodes, additional switches connected to said deiecting electrodes and arranged to connect said electrodes to the output of rst one, then the other of said receivers, and means for operating said rst mentioned switches and said additional switches in synchronism.

2. A radio direction nder including two loop antennas having their planes intersecting at 90, a pair of radio receivers including input connections and output connections, switches connected to said antennas and arranged to connect the respective antennas to rst one, then the other of said receiver input connections, a cathode ray tube including electrodes for deecting said ray along coordinates corresponding to said loop planes, additional switches connected to said deflecting electrodes and arranged to connect said switches and said additional switches.

3. A device of the character of claim 1 in Which 5 said receivers have diierent gain characteristics.

ERNST SCHULZ. 

